/  it  J;  if 


Issued  November  2;!,  1908. 


U.S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  PLANT  INDUSTRY— Circulai   No.  18. 
K.  T.  GALLOWAY,  Chief  of  Bureau! 


REAPPEARANCE  OF  A  PRIMITIVE  CHARACTER 
IN  COTTON  HYBRIDS. 


().   V.  COOK, 

BlONOMIST,   BUEEAI     OF    Pi, AM     InDI 


59001  -Clr.  is     08 


WASHINGTON  :  GOVERNMENT    PRINTING  Of-Fi.   I 


BUREAU  OF  PLANT  INDUSTRY. 

'  Pathologist,  and  Chief  of  Bureau,  Beverly  T.  Galloway. 
Physiologist  and  Pathologist,  and  Assistant  Chief  of  Bureau,  Albert  F.  Woods 

Laboratory  of  riant  Pathology,  Erwin  F.  Smith,  Pathologist  in  Cha 

Investigations  of  Diseases  of  Fruits,  Merlon  P..  Waite,   Pathologist  in  Charge. 

Laboratory  of  Forest  Pathology,  Haven  Metcalf,  Pathologist  in  <  barge. 

Cotton  an<i  TrucJc  Diseases  and  Plant   i"  ea  fill  '     0r1  m       athologlsl    in 

Charge. 
Plant  Life  i  westigations,  Walter  T.  Swingle,  Physiolo  harge. 

gallons,  Archibald  D,  Shamel  and  Daniel  N    Sho  ma   ei     Physiolo- 
gists in  Cha) 
Tobacco    Investigations,    Archibald    D.    Shamel,    Wightman    W.    Garner,    and    Ernest    II. 

MathSwson,  in  Charge. 
Corn   Investigations,  Charles  r.   Hartley,  Physj  i        arge. 

Ulcali  and  Drought   i         ;    tt   Plant   Breeding  Investigations,  Thomas  H.  Kearney,  Physl 
ologist  in  Cha  i 

\logy  and  Water  Purification   Investigations,  Karl  F.  Kellerman,  Physiologist 
in  <  'barge. 
Bionomic  Investigations  of  Tropical  and  Subtropical  Plants,  Orator   F.   Cook,   IKonomist 

in  Charge. 
Drug   and   Poisonous   Plant    Investigations   and    Tea    Culture   Investigations,    Rodney    H. 

True,  Physiologist  in  Charge. 
Physical  Laboratory,  Lyman  J.   Briggs,  Thysicist  in  Charge. 

Crop   Technology  and  Fiber  Plant   Investigations,   Nathan   A.  Cobb,  Crop  Technologist  in 
Charge. 

nvestigations,  Frederick  V.  Covill  iisi  in  Charge. 

ment   !  -  ations,  William  .1.  Spillman,  Agriculturist    in  charge. 

,  ations,  Mark  Alfred  Carleton,   Cerealist   in   Chai 

Hon  Experimental  Farm,  I."    i  t,  Horticulturist  in  Charge. 

Vegetable  Testing  Gardens,  William  W.  Tracy,  sr.,  Superintendent. 
Sugar-Beet  Investigations,  Charles  0.  Townsem  gist  in  charge. 

:,:,,.,,<„  al   Extension  Agriculturist  in  Charge. 

Di  '  ; culture  In  Chilcott,  Agriculturist  in  Charge. 

Pomological  Collections,  Gustavus  13.  Brackett,  Pomologist  in  Charge. 
Field  in  in  Pomology,  William  A.  Taylor  and  G.   Harold  Powell,   Penologists 

in  Charge. 

Gardens  and  Grounds,  Edward  M.  Byrnes,  Su]  lent. 

Foreign   Seed  and   Plant   Introduction,  David  Fairehild.   Agricultural    Explorer   in   Charge. 

,,   Crop  Investigations,  Charles  V.  Piper,  Agrostologisi  in  Charge. 
Scat  Laboratory,  Edgar  Brown,   B  i  Charge. 

lands   i  lation,  John  D.  Shanaban,   Crop  Technologist  in  Charge. 
Suui  Ernst  A.  Bessey,  Pal  In  Charge. 

,    ,,  ;,,.,/,    Hon  Garden,  Chico,  Cat.,  W.  W.  Tracy,  jr.,  Assistant  in  Charge. 

i-een,  Pomolog     t  i      CI 
Farmers'  Cooperative  Demonst  ati   n,  Worl  an  A.   Kn,  ent  in  Cha 

Seed   Distribution    (Directed  by  Chief  of  Bureau),   Lisle  Morrison,    Assistant    in   General 
Charge. 

Editor,  .1.  E.  Rockwell. 

Chit  (   Cirri;,   .lames   E.   Jones. 

ICir.   181 
2 


REAPPEARANCE  OF  A  PRIMITIVE  CHARACTER  IN 
COTTON  HYBRIDS. 


INTRODUCTION. 

The  facts  considered  in  this  brief  report  arc  incidental  result 
experiments  undertaken  for  the  purpose  of  acclimatizing  in  the 
United  States  weevil  resistant  varieties  of  cotton  from  Central 
America  and  of  hybridizing  them  with  our  United  States  varieties. 
The  experiments  have  not  yet  been  carried  far  enough  to  determine 
the  agricultural  value  of  these  varieties  in  the  United  States,  but  they 
have  already  afforded  several  facts  of  scientific  and  practical  ini 

li  is  demonstrated  that  hybrids  may  differ  from  both  parents  in 
showing  undesirable  primitive  characters  in  the  first  generation  and 
yet  may  be  free  from  such  characters  in  the  second  generation.  An 
explanation  of  this  strange  behavior  is  round  in  the  fact  that  the  first 
generation  of  hybrids  represents  an  intermediate  stage  in  the  pr< 
of  conjugation  begun  h\  the  original  germ  cells,  while  tin 
general  ion  is  formed  a  fter  a  plete  conjugation  has  taken  place. 

Thus  breeders  have  an  additional  reason  for  growing  their  hybrids 
for  a;  least  two  generations.     To  reject   lie  I  ation  hybrid:    be 

cause  they  appear  unpromising  is  to  judge  them  b(  •■  oeri 

mcni  of  crossing  is  really  complete.  It  i-  like  throwing  away  young 
plants  or  animal-  because  tiny  do  not  have  all  the  proper!  i 
adult-.  In-tead  of  being  accepted  a-  evidence  regarding  the  agri- 
cultural value  id'  hybrids  between  two  specie-  or  varieties  the 
acters  of  the  first  generation  ma\  be  merely  temporary.  Hybrids 
which  do  not  yield  a  desired  combination  of  parental  characters  in 
the  first  generation  may  siill  do  so  in  the  aeration. 

PRIMITIVE       CHARACTERS       SHOWN       IN       REVERSION       AND 
RECAPITULATION. 

Any  character  which  appear-  to  have  been  attained  i'ar  hack  in  the 
developmental  history  of  a  species  or  variety  may  he  described  as  a 
primitive  character.  The  name  i-  applied  re  especially  to  char- 
acters which  have  ceased  '"  be  regularly  expressed,  hut  come  to  light 
onl\  in  i  d  individual-  which  are  -aid  to  "  lake  after  '"  remote 
ancestoi              id  of  resembling  their  immediate  parents. 

Fad-  -how  ing  the  pei  istence  of  primitive  characters  in  plant-  and 
animals  are  commonly  recognized  as  constituting  two  distinct  group? 
of  phenomena,  called  reversion  and  recapitulation.  The  behavioi  ol 
[Clr  :■ 


4  A    PRIMITIVE    CHARACTER    IN    COTTON    HYBRIDS. 

our  cotton  hybrids  serins  to  show  that  the  relation  between  these 
phenomena  is  very  intimate,  and  that  one  may  pass  into  the  other 
us  a  result  of  hybridization. 

Reversion  is  the  reappearance  of  a  character  which  has  been  trans- 
mitted in  latent  form — that  is.  without  being  brought  into  expression 
in  the  parent  generation  or  in  a  previous  series  of  generations. 
Recapitulation  may  be  described  as  the  following  over  of  the  ances- 
tral paths  of  descent  in  each  generation.  Studies  of  the  embryology 
of  the  higher  vertebrates  have  shown  that  many  primitive  features 
are  brought  into  temporary  expression  in  the  course  of  development 
of  each  individual.  Mammalian  embryos  still  show  gill  clefts  and 
rudiments  of  other  ancestral  features  which  have  not  served  as  adult 
characters  for  many  geologic  ages. 

Reversion  and  recapitulation  have  no  limits  in  years  or  in  numbers 
of  generations.  They  give  us  a  vivid  indication  of  the  all-embracing, 
all-enduring  power  of  transmission.  Darwin  has  aptly  associated 
the  permanence  of  latent  characters  with  the  persistence  of  rudi- 
mentary organs : 

There  is  no  more  inherent  improbability  in  each  domestic  pig,  during  a  thou- 
sand generations,  retaining  the  capacity  and  tendency  to  develop  great  tusks 
under  fitting  conditions,  than  in  the  young  calf  having  retained  fur  an  indefinite 
number  of  generations  rudimentary  incisor  teeth,  which  never  protrude  through 
the  gums." 

In  this,  as  in  many  other  passages.  Darwin  recognizes  a  distinction 
which  many  subsequent  writers  have  overlooked,  perhaps  because 
no  definitely  contrasted  terms  were  used  to  define  it.  The  distinc- 
tion is  between  (1)  the  process  of  transmission  which  conveys  to 
successive  generations  of  organisms  the  '"capacity  and  tendency"  to 
reproduce  and  transmit  the  characters  of  their  parents  and  ancestors, 
and  (2)  the  process  of  expression,  by  which  characters  are  actually 
"  developed  "  or  worked  out  in  visible  form.  These  two  processes, 
transmission  and  expression,  give  us  the  facts  commonly  known  as 
"  heredity." 

Recapitulation  may  be  described  as  a  temporary  or  partial  expres- 
sion of  a  primitive  character,  while  reyersion  is  the  expression  of  a 
character  which  is  usually  transmitted  in  latent  form  without  coming 
into  expression  at  all.  Recapitulation  may  never  be  visibly  com- 
plete: many  ancestral  characters  are  not  brought  into  expression,  but 
the  power  of  such  characters  to  reappear  shows  that  they  continue 
to  he  transmitted.  The  '•capacity  and  tendency"  remain  in  the 
protoplasm,  even  when  no  visible  tissues  are  formed.  The  many 
different  reversions  shown  by  members  of  the  same  stock  indicate 
thai   all  the  ancestral  characters  are  probably  transmitted   ami  con- 


"  Darwin,  Charles.     Variation  of  Animals  and   Plants  under   Domestication, 
■hapter  13. 

[Cir.  isj 


\    PRI&IITIV1  CTEB  CI  ,     11\  BRIDS.  5 

tinue  to  be  capable  of  regaining  expi'ession  if  some  unusual  condi- 
tii  n  interferes  with  more  normal  com  ses  of  development.     Hybridi- 
zation and  transfer  to  new  conditions  are  the  most  familiar  meai 
calling  forth  the  latent  characters. 

The  course  of  development  followed  by  any  individual  plant  or 
animal  is  chosen,  as  it  were,  from  many  ancestral  alternatives. 
Though  only  tin'  chosen  characters  are  brought  into  expression,  the 
process  of  transmission  remains  inclusive  and  impartial.  Each  gen- 
eration is  to  be  thought  of  as  passing  along  to  I  essors  a  com- 
plete genealogical  chart,  (ialton's  law  of  regression  shows  that  each 
generation  tends  to  follow  the  route-,  used  by  the  parents  and  other 
recent  ancestors,  but  under  normal  conditions  of  descent  there  is  a 
wide  liberty  of  choice  Individual  diversity  rsistently  shown, 
even  when  organisms  of  the  same  ancestry  develop  under  the  same 
condition-. 

REAPPEARANCE   OF   GREEN   FUZZ   IN   COTTON   HYBRIDS. 

Reversion  is  often  reckoned  as  a  rare  and  exceptional  phenomenon, 
not  to  be  understoo  I  from  the  standpoint  of  normal  inheritance;  but 
the  fact  is  that  many  reversions  are  as  definite  and  uniform  as  any 
other  es  of  descent.     Thus  there  are  no  characters  in  which 

hybrids  between  the  Kekchi  cotton  of  Guatemala  and  the  Sea-Island 
or  Egyptian  cotton-  are  in  better  agreement  than  in  the  very  large 
size  of  the  seeds  and  in  the  det    e  coat  of  bluish  green  fuzz  with  which 
eeds  arc  covered  underneath  the  long,  while  lint.     These  ch 

the  seeds  of  the  hybrids  abruptly  different    from  those 
of  the  parent  typ<   . 

The  removal  of  the  lint  leave-  the  seeds  of  the  Kekchi  cotton  i 
ered  with  a  dense  white  fuzz,  while  the  seeds  of  the  Sea-Island  and 
Egyptian  cottons  are  black  and  naked.  Thus  the  green  fuzz  of  the 
hybrid  seed  is  not  a  blend  or  other  combination  of  the  parental  char- 
acter-, though  it  may  be  viewed  as  a  compromise  between  the  paren- 
tal condition-  if  considered  in  relation  to  other  facts  of  n 
and  recapitulation.  Examples  of  green  fuzz  are  found  in  many  dif- 
i  :  pes  of  cotton,  including  those  which  are  native  in  the  Old 
World,  and  especially  in  wild  or  unimproved  varieties.  Thus  it 
probably  represents  an  ancestral  condition  from  which  both  of  tic 
parental  types  have  diverged.  No  wild  cottons  with  white  fuzz  seem 
i"  I"  known,  hut  most  of  the  naked-seeded  cotton-  have  a  small  tuft 
of  green  or  brown  fuzz  at  the  base  of  tl  itemalan  cot 

ton  of  dp  Sea-Island  -eric-  has  the  lower  half  of  the  seed  coated 
with  green  fuzz,  the  Inn  being  confined  to  the  upper  half,  which 
has   no  fuzz.0 


Cook,  O.  r.     Weevil  Resisting  Adaptations  of  the  Cotton  I'ftuit,  [Juliet iu  88, 
mi  of  1  'lu  111  Industry,  l  .  S.  Dept    "i  ure,  \<.  32. 


b  A    PRIMITIVE    CHARACTER   IK    COTTOK    HYBRIDS. 

The  reappearance  of  the  green  fuzz  in  these  hybrids  need  not  be 
considered  as  a  turning  back  from  the  characters  of  the  parent 
varieties,  as  the  word  reversion  seems  to  imply.  These  hybrids  do 
not  follow  either  of  the  parental  routes  of  development,  but  com- 
promise on  a  primitive  character  which  appears  to  represent  common 
ancestral  ground.  A  stage  of  development  which  is  quickly  passed 
by  or  entirely  latent  in  the  parent  varieties  remains  as  a  definitely 
expressed  character  of  the  hybrids.  Abortive  seeds  are  often  found 
with  green  fuzz,  even  when  normally  matured  seeds  in  the  same 
locks  have  white  fuzz.  Thus  reversions  can  be  viewed  as  conditions 
of  arrested  development— failures  to  pass  beyond  stages  marked  by 
primitive  characters. 

DIFFERENCES  BETWEEN  FIRST  AND  SECOND  GENERATIONS. 

The  recali  to  expression  of  the  ancestral  green-fuzz  character  is  not 
permanent.  The  next  generation  shows  a  wide  diversity  of  combina- 
tions and  intergradations  between  the  characters  of  the  parent  types, 
but  there  is  no  such  failure  to  attain  the  parental  characters  as  in  the 
first  generation,  though  the  green  color  sometimes  remains  in  the 
second  and  even  in  the  third  generation.  Why  an  ancestral  character 
should  so  regularly  appear  in  the  first  generation  and  almost  as  regu- 
larly disappear  in  the  second  is  not  easiby  understood  until  we  remem- 
ber that  the  second  generation  is  the  first  that  represents  a  completion 
of  the  conjugation  begun  by  the  original  germ  cells." 

The  first  generation  is  formed  during  the  preliminary  stages  of 
conjugation,  so  that  the  temporary  expression  of  an  ancestral  char- 
acter in  the  first  generation  may  not  be  essentially  different  from 
other  phenomena  of  recapitulation  in  which  temporary  expression  of 
characters  takes  place.  Instead  of  an  intermediate  average  between 
the  divergent  parental  characters  or  the  dominance  of  one  over  the 
other,  the  green  fuzz  may  represent  a  third  method  of  adjusting 
the  parental  differences,  by  compromising  upon  a  common  ancestral 
character. 

If  we  think  of  the  green  fuzz  as  in  the  nature  of  a  chemical  com- 
bination of  the  parental  characters,  its  failure  to  become  "fixed" 
appears  very  mysterious;  but  when  we  associate  it  with  the  phe- 
nomena of  reversion  and  recapitulation  it  is  easy  to  understand  that 
the  disappearance  of  the  green  in  the  second  generation  accords  with 
the  very  frequent  result  that  the  second  generation  of  a  hybrid  differs 
from  the  first.  An  intermediate  and  nearly  uniform  first  generation 
often  produces  an  extremely  diversified  second  generation. 

The  experiments  of  Mendel  and  his  successors  have  made  us 
familiar  with  the  fact  that  parental  characters  which  are  suppressed 

"Cook,  <».  !•'..  and  Swingle,  W.  'I'.     Evolution  of  Cellular  Structures,  Bulletin 
81,  Bureau  of  Planl  Industry,  '■'•  S.  Dent,  of  Agriculture,  190.". 
[Clr  IS] 


RIMI  I  IVl.   cil  ai:  \c  ill;    I  :•     CO!        -     i^  BR1DS.  i 

in  the  first  generation  commonly  reappear  in  th<  '  generation. 

of  a  Mendelian  hybrid  shows  only  oi  •  of  a 
of  contra  irental  characters   (called  the  dominant  chara< 

btil  the  other  characl  a  part  of  the 

generation.     The  fuzz  character  may  be  de- 

scribed a  typical  .  for  a  ■ 

linen!  in  th<  ration  tends  to  disappear  in  I 

itions.      I  true  c.  i  •  tween  the  wiii 

Kekchi  cotton  a  pland  \  .  like  the 

Truitt.    Though  the  \  linates  in  the  first 

ation,  it  gradually  hird  genera 

I   simila  dendelian  behavior  is  shown 

in  a   hybrid   in   which  th  i  to  be 

dominant  in  i  ion,  while  about  two-thirds  of  the  plains 

of  thi  I  generation  have  tl  different  degrees. 

In  a  lev.  of  them  the  fuz  h,  but  none  have  the  vivid  green 

usually  shewn  when  the  color  appears  in  the  fii  ation. 

EXPRESSION    OF    CHARACTERS    IN    FIRST    AND    SECOND 
GENERATIONS. 

Diffi  between  the  first  and  second  generations  of  hybrids  are 

the  externa]  evidence  of  the  fact  that  th  esses  of  reprodui 

followed  by  the  higher  plant-  and  animal-  have  two  critical  points 
or  periods  of  adjustment  of  the  internal  relations  which  govern  the 
expressions  of  the  character-.  One  adjustment  is  made  when  conju- 
gation begins  by  the  union  of  the  outer  protoplasm  and  nuclei  of  the 
two  germ  cells.  A  second  adjustment  is  made  when  conjugation  is 
completed  by  the  fusion  of  the  chromatic  material  of  the  cells  (mitap- 
sis)  before  the  formation  of  the  gi  ;is  which  give  rise  to  the  sec 

ond  generation.     The  adjustn  lade  when  the  conjugation  of  the 

germ  cells  begins  are  usually  less  profound  than  those  accomplished 
when  i    n  n  is  completed. 

The  first  adjustment  has  the  single  result  of  determining  the  ex- 
pression of  characters  in  the  fir  i  generation— that  in  which  the  con- 
jugation begin-.  The  r<  suits  of  the  second  adjustment  are  not  shown 
until  the  second  generation,  which  i-  in  reality  the  first  generation  to 
be  formed  after  conjugation  has  been  completed  by  mitapsis.  The 
second  gi  hows  a  very  different  series  of  adjustments, 

and  often  a  widely  varied  series.     Individual  members  of  (his  gen 
(•ration    frequently    differ   as   much    from   each   other   as   from   the 
parental  ty] 

If  characters  combined  like  other  physical  or  chemical  substances 
we  might  expect  that  like  ingredient-  would  produce  like  results, 
whereas  hybrids  of  the  same  parentage  may  be  endlessly  diverse. 

[Cil 


8  A    PRIMITIVE   CHARACTER   IN    COTTON    HYBRIDS. 

The  facts  of  reversion  and  recapitulation  enable  us  to  look  upon  these 
diversities  of  hybrids  as  corresponding  to  the  normal  diversities  of 
descent  of  the  parental  groups  intensified  by  the  recall  to  expression 
of  ancestral  peculiarities,  such  as  the  green  fuzz  of  the  cotton  hybrids. 

If  the  green-fuzz  character  behaved  in  a  truly  Mendelian  manner 
half  of  the  second  generation  would  have  green  seeds.  The  theory  of 
Mendelism  holds  that  characters  are  transmitted  as  separate  "  units  " 
and  that  the  units  which  represent  definitely  contrasted  parental 
characters  pass  into  separate  germ  cells  at  the  end  of  the  first  genera- 
tion. Thus  the  germ  cells  formed  by  the  green-seeded  first  genera- 
tion would  carry  either  the  black-seeded  Egyptian  character  or  the 
while-seeded  Kekchi  character.  Half  of  the  germ  cells  would  con- 
jugate with  others  of  their  own  kind  and  half  would  find  mates  of  the 
opposite  kind.  The  contrasted  pairs  would  give  rise  to  green-seeded 
plants,  while  the  other  half  of  the  second  generation  would  be  equally 
divided  between  white  seeds  and  black  seeds. 

The  general  disappearance  of  the  green  seeds  in  the  second  genera - 
tion  indicates  that  the  germ  cells  which  produce  this  generation  do 
not  have  the  same  expression  relations  as  those  which  produced  the 
first  generation,  for  there  is  not  the  same  tendency  to  recall  the  green 
fuzz  into  expression.  Development  no  longer  halts  at  this  earlier 
stage,  but  brings  back  the  white  fuzz  and  the  smooth  seeds  of  the 
parent  types  and  many  intermediate  conditions.  The  parental  charac- 
ters are  not  only  united  with  each  other  in  varying  combinations,  but 
also  in  combination  with  occasional  traces  of  the  green  fuzz  or  of 
brown  fuzz,  a  character  which  also  appears  in  primitive  types  of 
cotton.  Traces  of  green  or  brown  fuzz  may  even  arrive  without 
hybridization,  as  when  the  Kekchi  cotton  is  being  raised  for  the  first 
time  in. the  United  States,  or  when  our  Upland  varieties  are  grown  in 
new  localities.  Exposure  to  new  conditions  disturbs  the  usual  course 
of  development  and  brings  many  latent  diversities  into  expression, 
often  the  same  diversities  that  are  found  among  the  hybrids. 

Different  crosses  between  the  same  stocks  may  show  different  de- 
crees of  expression  of  the  green  character.  Sometimes  it  does  not 
appear  in  (he  first  generation  and  sometimes  it  lingers  in  a  large 
proportion  of  the  second  generation.  The  strongest  tendency  to 
retain  the  green  fuzz  has  been  noticed  in  a  hybrid  which  had  the 
Jannovitch  Egyptian  cotton  Tor  the  female  parent  and  the  Kekchi 
cotton  for  the  male  parent.  In  one  planting  of  thirty  second-genera- 
tion individuals  raised  from  a  green-seeded  plant  of  the  firsl  genera- 
tion, twenty  show  at  least  a  trace  of  green  in  the  fuzz,  five  have  the 
seeds  nearly  smooth,  and  five  others  have  them  densely  covered  with 
white  fuzz.  Among  the  twenty  reckoned  as  having  green  seeds  there 
are  many  gradations  in  the  color  as  well  as  in  the  amount  of  fuzz 
on  the  seeds. 

fCiv.  IS] 


a    PRIMITIVK    CHAKACTER    IN    COTTOfl     HYBR  9 

EXPRESSION  OF  CHARACTERS  DETERMINED  BY  ADJUSTMENTS. 

It  is  not  necessary  to  suppose  that  the  return  of  the  parental  char 
acters  in  the  second  generation  of  the  cotton  hybrids  is  caused  l>y  a 
mere  reversal  or  undoing  of  the  internal  adjustments  which  led  to 
the  formal  ion  of  the  green  seeds,  as  the  theory  of  Mendelism 
sumes.  The  probability  is  rather  thai  the  parental  characters  return 
because  further  and  more  complete  adjustments  have  been  reached. 
Even  from  the  standpoint  of  Mendelism  it  has  to  be  recognized  for 
the  6rs1  generation  that  the  expression  relations  of  the  characters  are 
determined  by  adjustment. 

There  is  no  reason  to  believe  that  either  of  the  germ  cells  which  have 
formed  one  of  the  green-seeded  hybrids  was  adjusted  to  bring  the 
green-seed  character  into  expression.  The  green-seed  character 
would  have  continued  to  remain  in  abeyance  if  either  of  the  germ  cells 
which  give  rise  to  a  green-seeded  hybrid  had  conjugated  with  a  part- 
ner of  its  own  kind.  Bui  after  the  conjugation  began,  the  tendencies 
o\'  expression  we]  i  changed  and  the  green-seeded  character  appeared. 

I  rider  the  theory  of  .Mendelism  two  different  assumptions  are  i 
in  attempting  to  explain  the  two  changes  of  characters,  away  from  the 
parents  and  then  back  again.  It  has  to  be  considered  that  the  char- 
acters of  the  first  generation  are  determined,  as  stated,  by  a  readjust- 
ment of  the  internal  relations  which  govern  the  expression  of  the 
characters.  But  when  the  end  of  the  generation  is  reached  and  new 
,:i  cells  arc'  to  be  formed  .Mendelism  assumes  that  the  expression 
relations  oil  iie  new  cells  are  determined  in  another  and  very  different 
way.  by  the  segregation  of  the  "units"  of  the  contrasted  parental 
characters  in  distinct  germ  cells. 

The  assumptions  of  Mendelism,  that  the  characters  are  represented 
by  "•  unit-  "  and  that  these  are  segregated  and  are  transmitted  by  dif- 
ferent verm  cell-,  become  unnecessary  as  soon  as  we  consider  that  the 
expression  relations  of  germ  cells  may  be  determined  by  adjustment. 
The  fact  that  the  expression  relations  of  germ  cell-  are  capable  of 
being  readjusted  after  conjugation  should  lie  considered  as  evidence 
that  the  relations  they  have  before  conjugation  are  also  reached  by 
adjustment  rather  than  by  exclusion.  If  char  icters  are  to  be  thoughl 
ented  in  the  germ  cell-  by  definite  particles  or  material 
"units"  ;    kind,  it  is  more  in  accord  e  fads  to  think  of 

hanging  some  positional,  chemical,  or  other  rela- 
tion among  themselves  than  a-  being  separately  transmitted  in  dif 
ferent  germ  cells. 

Such  fact-  a-  the  reappearance  of  the  green  fuzz  in  the  first  genera 
tion  of  these  cotton  hybrids  show  that  the  readjustment  of  expression 
relations  in  the  first  generation  i-  not  confined  to  the  parental  char 
acters,  hut  maj   involve  the  recall  to  expression  of  primitive  charac 

[Or   18] 


10  \    PRIMITIVE   CHARA<    I     B       ■    COTTON     BYBRIDS. 

lers  transmitted  in  latent  form  from  remote  ancestors.  It.  is  one  of 
many  indications  that  the  changes  of  expression  relations  which  have 
to  be  ascribed  to  adjustment  are  quite  as  great  as  those  which  Men- 
delism  has  sought  to  explain  by  the  theory  of  "character  units'1  and 
•  .    heir  segregation  in  "  pure  germ  cells." 

Writers  on  Mendel  ism  have  sought  to  connect  the  idea  of  a  separa- 
tion of  character  units  with  the  processes  of  subdivision  by  which  the 
germ  cells  are  formed.     The  fact  that  four  germ  cells  are  formed  by 
ividing  one  mother  cell  has  led  to  the  s  on  that  a  separa- 

tion of  antagonistic  character  units  might  occur  when  this  subdivi- 
sion takes  place.  Two  of  the  germ  cells  might  contain  the  "unit*1 
representing  one  of  the  contrasted  characters  and  two  other  'germ 
cells  the  unit  of  the  other  character.  This  would  give  equal  num- 
bers of  germ  cells  of  the  two  kinds  which  the  theory  of  Mendelism 
lires.  Nevertheless  it  is  possible  for  this  equality  to  be  reached 
in  another  more  practical  way.  The  numbers  of  germ  cells  tending 
to  express  the  contrasted  characters  will  be  equal  if  equal  numbers 
of  the  mother  cells  become  adjusted  in  the  two  ways  before  subdi- 
vision into  germ  cells  takes  place.  Thus  all  the  germ  cells  from  the 
same  mother  cell  may  be  of  the  same  kind  instead  of  being  of  two 
kinds.  This  view  is  more  practical  because  it  does  not  require  us 
to  suppose  that  the  mother  cells  divide  into  unequal  parts  in  forming 
germ  cells.  In  view  of  the  frequency  of  the  phenomena  of  rever- 
sion and  recapitulation  it  is  much  easier  to  suppose  that  both  of  the 
'•ontrasted  characters  are  transmitted,  though  only  one  comes  into 
expression,  than  to  believe  that  then-  is  any  separate  transmission  of 
character  units  in  different  germ  cells. 

SIGNIFICANCE  OF  PRIMITIVE  CHARACTERS  IN  BREEDING. 

Breeders  will  appreciate  the  practical  importance  of  the  fact  that 
such  a  character  as  the  green  fuzz  of  cotton  is  not  necessarily  perma 
nent,  even  though  it  may  be  shown  by  all  the  members  of  the  first 
generation  of  a  hybrid.  A>  soon  as  we  know  that  such  a  character 
is  likely  to  disappear  we  recognize  the  need  of  carrying  our  hybrids 
over  to  the  second  and  third  generations  before  undertaking  to  make 
final  determinations  of  their  merits. 

Even  among  the  cotton  hybrids  it  has  to  be  considered  that  other 
and  more  important  characters  may  be  affected  by  the  same  prin- 
ciples as  the  green  fuzz.  In  the  first  generation  all  the  hybrids  be- 
tween the  Central  American  types  of  cotton  and  our  improved  Upland 
varieties  produced  shorter  lint  than  either  of  the  parents.  If  the 
short  lint  had  been  looked  upon  as  a  permanent  character,  such  liv 
brids  would  have  been  rejected  as  of  no  value  in  comparison  with 
the  parent  varieties.  Nevertheless,  a  series  of  these  hybrids  is  being 
retained  in  order  to  learn  whether  the  short  lint  will  not  behave  like 

Kir   18] 


A    PRIMH  IVE   CHARACTJ  11 

a  primitive  character  and  give  place  to  long  lint,  in  later  generations. 
Indeed,  this  seems  already  to  he  taking  place.     Though  th  lint 

-  not  disappear  as  promptly  a  sjreen  fuzz,  the  second  and 

third  generations  of  the  hybrids  are  showing  examples  of  much  lorn 
lint  than  appeared  in  the  first  g(  neration. 

SUMMARY. 

hi  hybrids  between  the  Kekchi  ■  temala  and  varieties 

of  tin-  Sea-Island  and  Eg}  ptian  nly  show  gr 

fuzz  in  the  ration.     This  character  does  not  normally  app 

in  either  of  the  parental  varieties,  though  it  is  probably  an  ancestral 
character  of  both  of  them. 

The  reappearance  of  the  primitive  character  in  the  hybrids  is  to 
he  associated   with  other   facts  of   reversion  and  recapitulation,  and 
io  indicate  that  these  groups  of  phenomena  are  very  closely 
related. 

The  fact  that  the  green  fuzz  largely  disappears  in  the  second  gen- 
eration of  the  hybrids  indicate-  that  the  recall  of  this  character  to 
expression  in  the  firsl  generation  marks  a  preliminary  stage  in  the 
process  of  conjugation.  The  complete  results  of  conjugation  first  be- 
come visible  in  the  second  generation,  when  the  parental  characters 
reappear  in  many  combinations  and  gradations.  By  thus  recognizing 
that  th"  firsl  and  second  generations  of  hybrids  represent  different 
stages  of  the  process  of  conjugation  it  is  possible  to  understand  the 
appearance  and  disappearance  of  such  characters  as  the  green  fuzz 
without  resorting  to  the  complicated  theory  of  Mendelism. 

The  practical  point  is  that  such  departures  from  the  parental  char- 
acter- in  the  first  generation  of  a  hybrid  may  not  remain  to  detract 
from  the  value  of  later  generations.  Hybrids  in  which  these  undesir- 
able primitive  character-  come  int  -ion  must  be  grown  for  at 
least  two  generations  before  -election  can  be  effectively  applied.  The 
characters  shown  by  the  first  generation  do  not  afford  any  practical 
indication  regarding  the  characters  of  the  later  generations. 

Approved  : 

James  Wilson, 

n  tary  <>i  .  Vgricultun  . 

Washington,  D.  ('..  October  /.'.  1908. 

[Clr.  18] 


iMivtKSi  i  y   Oh   FLORIDA 


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